1. Field of the Invention
The present invention relates to a map display apparatus associated with a navigation system used as a travel-assisting system for cars or other vehicles.
2. Description of the Related Arts
In recent years, car navigation systems using, for example, GPS (Global Positioning System: A system which computes the position of one's vehicle using vehicle position information sent from a satellite), have been constructed as assisting systems for cars or other vehicles to carry out navigation to the vehicle's destination. In general navigation systems, navigation has been carried out by displaying on an LCD (Liquid Crystal Display) and other map display apparatus map information stored in an external storage device such as a CD-ROM, routes previously input by the user, together with the position of the vehicle obtained from the GPS. A conventional map display apparatus will be hereunder described.
FIG. 8 is a block diagram of the functional parts of a conventional map display apparatus. Reference numeral 81 denotes an input means by which the user inputs the routes; reference numeral 82 denotes an external storage device such as the CD-ROM in which the map information is stored; reference numeral 83 denotes an information read-out means for reading out the map information stored in the map information storage device 82; reference numeral 84 denotes a means for computing the present position of the vehicle by the GPS or and other such travel-assisting systems; and reference numeral 85 denotes a display means for displaying the desired map information at any scale arbitrarily selected by the user, with the present position of the vehicle computed by the means 84 for computing the present position of the vehicle located in the center of the displayed map.
The flow of operations carried out in the conventional map display apparatus having the above-described structure will be described with reference to the flow chart in FIG. 9. First, the user searches the map information, including the route starting point S, by use of the map information storage means 82 for displaying the map on the display means 85 at a scale arbitrarily selected by the user (Step 90). The user then uses the input means 81 to input the route starting point S, passing points P1, P2, . . . , and point of destination E on the displayed map in accordance with the route order intended to be taken by the user (Step 91), thereby completing the input of the routes.
After starting the navigation of the vehicle, the user then uses the means 84 for computing the vehicle's present position, such as the GPS, to compute the present position of the vehicle (Step 92). The user displays the road information map showing the computed result at an easily readable map scale on the display means 85, with the present position of one's vehicle being at the center thereof (Step 93). The vehicle is navigated by repeating Steps 92 and 93 until the response to the question posed in Step 94 (Destination E Reached?) is yes, in accordance with the operations input in Step 91.
An example of an actual map displayed on the screen of a conventional display apparatus will be described with reference to FIG. 10. Reference numeral 101 denotes a mark indicating one's own vehicle; and reference numeral 102 denotes one of the passing points P input in Step 91 by means of the input means 81. During navigation, the map is displayed on a display means 85 at a scale which allows easy reading of the roads of the area around the center of the map, where the present position of the moving car is located. If the user wants to know the routes which he has taken up to the present time, or if he wants to have a general view of the routes he will take, he needs to change the scale of the displayed map to that which shows all the routes. In addition, after confirming the routes, the scale of the map must be changed to that showing the most detailed road features of the area around the present position of the moving vehicle.
As described above, the conventional map display apparatuses have problems which require the user to change the scale of the map displayed on the display means to that which shows all the routes every time the user wants to know the routes he has taken up to the present time or when he wants to have a general view of the routes he will take. The user is also required, after confirming the routes, to return the scale of the map back to that which shows the greatest detail of the roads of the area around the present position of the moving vehicle.